A simple and sensitive ion chromatography method was developed, optimized and validated for the determination of Monomethylamine (MMA) in various drug substances, which is the process impurity. The validation of analytic method was realized through specificity, linearity, LOD, LOQ, precision and accuracy parameters. A model compound, Tadalafil drug substance was chosen for this study and limit of detection (LOD) and limit of quantification (LOQ) values were 0.09 μg/mL and 0.30 μg/mL respectively. The average accuracy value is 101.6%. And also determination of MMA in different drug substances like Alfuzosin hydrochloride, Sumatriptan succinate, Sertraline hydrochloride and Didanosine with slight modifications in methodology were discussed in this work